4,268 research outputs found
The impact of the warm outflow in the young (GPS) radio source & ULIRG PKS 1345+12 (4C 12.50)
(Abridged) We present new deep VLT/FORS optical spectra with intermediate
resolution and large wavelength coverage of the GPS radio source and ULIRG
PKS1345+12 (4C12.50; z=0.122), taken with the aim of investigating the impact
of the nuclear activity on the circumnuclear ISM. PKS1345+12 is a powerful
quasar and is also the best studied case of an emission line outflow in a
ULIRG. Using the density sensitive transauroral emission lines [S II]4068,4076
and [O II]7318,7319,7330,7331, we pilot a new technique to accurately model the
electron density for cases in which it is not possible to use the traditional
diagnostic [S II]6716/6731, namely sources with highly broadened complex
emission line profiles and/or high (Ne > 10^4 cm^-3) electron densities. We
measure electron densities of Ne=2.94x10^3 cm^-3, Ne=1.47x10^4 cm^-3 and
Ne=3.16x10^5 cm^-3 for the regions emitting the narrow, broad and very broad
components respectively. We calculate a total mass outflow rate of 8 M_sun
yr^-1. We estimate the total mass in the warm gas outflow is 8x10^5 M_sun. The
total kinetic power in the warm outflow is 3.4x10^42 erg s^-1. We find that
only a small fraction (0.13% of Lbol) of the available accretion power is
driving the warm outflow, significantly less than currently required by the
majority of quasar feedback models (~5-10\% of Lbol), but similar to recent
findings by Hopkins et al. (2010) for a two-stage feedback model. The models
also predict that AGN outflows will eventually remove the gas from the bulge of
the host galaxy. The visible warm outflow in PKS1345+12 is not currently
capable of doing so. However, it is entirely possible that much of the outflow
is either obscured by a dense and dusty natal cocoon and/or in cooler or hotter
phases of the ISM. This result is important not just for studies of young
(GPS/CSS) radio sources, but for AGN in general.Comment: Accepted for publication in MNRAS. 11 pages, 4 figure
Is Centaurus A special? A neutral hydrogen perspective
Due to the proximity, the neutral hydrogen belonging to Centaurus A can be
observed at high resolution with good sensitivity. This allows to study the
morphology and kinematics in detail in order to understand the evolution of
this radio-loud source (e.g. merger history, AGN activity). At the same time,
it is important to compare the results to other sources of the same class (i.e.
early-type galaxies in general and radio galaxies in particular) to see how
Centaurus A fits into the global picture of early-type/radio galaxy evolution.
The amount of HI, the morphology of a warped disk with HI clouds surrounding
the disk and the regular kinematics of the inner part of the HI disk are not
unusual for early-type galaxies. The growing evidence that mergers are not
necessarily responsible for AGN activity fits with the observational result
that the recent merger event in Centaurus A is not connected to the current
phase of activity. Based on these results, we conclude that Centaurus A has
typical neutral hydrogen properties for an early-type and radio galaxy and it
can therefore - from an HI perspective - be seen as a typical example of its
class.Comment: submitted to PASA; 7 pages, 4 figure
Fast Outflows of Neutral Hydrogen in Radio Galaxies
AGN activity is known to drive fast outflows of gas. We report the discovery
of fast outflows of neutral gas with velocities over 1000 km/s in a number of
radio galaxies. In the best studied object, 3C~293, the kinematical properties
of the neutral and ionised outflows are similar, indicating a common origin.
Moreover, the outflow appears to be located near the radio lobes and not near
the nucleus. This suggests that the interaction between the radio jet and the
ISM is driving the outflow.Comment: To appear in the proceedings of IAU Symposium 222,"The Interplay
among Black Holes, Stars and ISM in Galactic Nuclei", eds Storchi-Bergmann et
al; 2 pages, 1 figur
Gas outflows in radio galaxies
We present a summary of our recent results on gas outflows in radio galaxies.
Fast outflows (up to 2000 km/s) have been detected both in ionized and neutral
gas. The latter is particularly surprising as it shows that, despite the
extremely energetic phenomena occurring near an AGN, some of the outflowing gas
remains, or becomes again, neutral. These results are giving new and important
insights on the physical conditions of the gaseous medium around an AGN.Comment: To appear in the proceedings of the IAU Symposium #217, Recycling
Intergalactic and Interstellar Matter, eds. P.-A. Duc, J. Braine, and E.
Brinks, 6 pages. The full paper with high resolution images can be downloaded
from http://www.astron.nl/~morganti/Papers/outflows.ps.g
IC5063: AGN driven outflow of warm and cold gas
We present new ATCA 17- and 24-GHz radio images and ESO-NTT optical spectra
of the radio-loud Seyfert galaxy IC5063, the first galaxy in which a fast (~
600 km/s) outflow of neutral hydrogen was discovered. The new radio data
confirm the triple radio structure with a central core and two resolved radio
lobes. This implies that the previously detected fast outflow of neutral gas is
occurring off-nucleus, near a radio lobe about 0.5 kpc from the core. The
ionised gas shows complex kinematics in the region co-spatial with the radio
emission. Broad and blueshifted (~ 500 km/s) emission is observed in the region
of the radio lobe, at the same location as the blueshifted HI absorption. The
velocity of the ionised outflow is similar to the one found in HI. The first
order correspondence between the radio and optical properties suggests that the
outflow is driven by the interaction between the radio jet and the ISM. Despite
the high outflow velocities, no evidence is found for the ionisation of the gas
being due to fast shocks in the region of the outflow, indicating that
photoionisation from the AGN is likely to be the dominant ionisation mechanism.
The outflow rate of the warm (ionised) gas is small compared to that of the
cold gas. The mass outflow rate associated with the HI is in the same range as
for ``mild'' starburst-driven superwinds in ULIRGs. However, in IC5063, the
AGN-driven outflow appears to be limited to the inner kpc region of the galaxy.
The kinetic power associated with the HI outflow is a small fraction (a few x
10^-4) of the Eddington luminosity of the galaxy but is a significant fraction
(~ 0.1) of the nuclear bolometric luminosity. In IC5063, the outflows may have
sufficient kinetic power to have a significant impact on the evolution of the
ISM in the host galaxy.Comment: Accepted for publication in A&A, 11 pages, 8 figure
The optical morphologies of the 2Jy sample of radio galaxies: evidence for galaxy interactions
We present deep GMOS-S/Gemini optical broad-band images for a complete sample of 46 southern 2Jy radio galaxies at intermediate redshifts (0.05<z<0.7). Based on them, we discuss the role of galaxy interactions in the triggering of powerful radio galaxies (PRGs). The high-quality observations presented here show for the first time that the overall majority of PRGs at intermediate redshifts (78-85%) show peculiarities in their optical morphologies at relatively high levels of surface brightness(˜μV = 23.6 mag arcsec−2; μV ≃ [21, 26] mag arcsec−2). The observed morphological peculiarities include tails, fans, bridges, shells, dust lanes, irregular features, amorphous haloes, and multiple nuclei. While the results for many of the galaxies are consistent with them being observed at, or after, the time of coalescence of the nuclei in a galaxy merger, we find that more than one-third of the sample are observed in a pre-coalescence phase of the merger, or following a close encounter between galaxies that will not necessarily lead to a merger. By dividing the sample into Weak-Line Radio Galaxies (WLRGs; 11 objects) and Strong-Line Radio Galaxies (SLRGs; 35 objects) we find that only 27% of the former show clear evidence for interactions in
their optical morphologies, in contrast to the SLRGs, of which at least 94% appear interacting. This is consistent with the idea that many WLRGs are fuelled/triggered
by Bondi accretion of hot gas. However, the evidence for interactions and dust features in a fraction of them indicates that the accretion of cold gas cannot always be ruled out. Of the 28% of the sample that display evidence for significant starburst activity, we find that 92% present disturbed morphologies, following the same general trend as the total and SLRG samples. By comparing our PRGs with various samples of quiescent ellipticals from the literature, we conclude that the percentage of morphological
disturbance that we find here exceeds that found for quiescent ellipticals when similar surface brightnesses are considered. Overall, our study indicates that galaxy
interactions are likely to play a key role in the triggering of AGN/jet activity
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